Organized assemblies of single wall carbon nanotubes and porphyrin for photochemical solar cells. Charge injection from excited porphyrin into single-walled carbon

Photochemical solar cells have been constructed from organized assemblies of single-walled carbon nanotubes (SWCNT) and protonated porphyrin on nanostructured SnO2 electrodes. The protonated form of porphyrin (H4P2+) and SWCNT composites form 0.5−3.0 μm-sized rodlike structures and they can be assembled onto nanostructured SnO2 films [optically transparent electrode OTE/SnO2] by an electrophoretic deposition method. These organized assemblies are photoactive and absorb strongly in the entire visible region. The incident photon to photocurrent efficiency (IPCE) of OTE/SnO2/SWCNT-H4P2+ is ∼13% at an applied potential of 0.2 V versus saturated calomel electrode. Femtosecond pump−probe spectroscopy experiments confirm the decay of the excited porphyrin in the SWCNT−H4P2+ assembly as it injects electrons into SWCNT. The dual role of SWCNT in promoting photoinduced charge separation and facilitating charge transport is presented.